Optical data storage media and methods for using the same

ABSTRACT

An optical data storage medium is provided. The optical data storage medium includes a polymer matrix; a reactant capable of undergoing a change upon triplet excitation, thereby causing a refractive index change; and a non-linear sensitizer capable of absorbing actinic radiation to cause upper triplet energy transfer to said reactant. The refractive index change capacity of the medium is at least about 0.005. The non-linear sensitizer comprises a triarylmethane dye.

BACKGROUND

The present disclosure relates to optical data storage media. Moreparticularly the present disclosure relates to holographic storage mediaas well as methods of making and using the same.

The rapid growth of information technology industry has led to anincreasing demand for data storage systems. Optical data storage,wherein reading or writing of data is accomplished by shining light on,for example a disc, provides advantages over data recorded in mediawhich must be read by other means, for example a magnetically sensitivehead for reading magnetic media, or a needle for reading media recordedin vinyl. And, more data can be stored in smaller media optically thancan be stored in vinyl media. Further, since contact is not required toread the data, optical media are not as vulnerable to deterioration overperiods of repeated use as vinyl media.

Nonetheless, conventional optical data storage media does havelimitations as known to one skilled in the art. Alternative data storagemethods include holographic storage. This is an optical data storagemethod in which the data is represented as holograms. Early attempts atholographic storage relied on a page-based approach, i.e., where thebits of digital information are encoded into volume holograms astwo-dimensional arrays of logical zeros and ones that traversed a‘slice’ of the necessarily linear media onto which the holograms wererecorded. More recent research into holographic data storage has focusedon a bit-wise approach, where each bit (or few bits) of information isrepresented by a hologram localized to a microscopic volume within amedium to create a region that reflects the readout light. Materialscapable of accommodating a bit-wise data storage approach are highlysought after as the equipment utilized to read and write to suchmaterial is either currently commercially available, or readily providedwith modifications to readily commercially available reading and writingequipment. Further, holographic data storage by the bit-wise approach ismore robust to temperature, wavelength, intensity variations, andvibration than holographic data stored using the page-based approach. Inorder to be optimally useful in the recordation of holograms, and inparticular, micro-holograms, bit-wise data storage materials must benon-linear and further exhibit desirable refractive index change inresponse to recording light. The magnitude of the refractive indexmodulations produced in the material by the recording light defines thediffraction efficiency for a given system configuration, whichtranslates to the signal to noise ratio, bit error rate, and theachievable data density.

Thus, there remains a need for optical data storage media that canexhibit a nonlinear (or “threshold”) response to the recording lightintensity and that is suitable for bit-wise holographic data storage. Inparticular, it would be advantageous for holograms stored in the mediato be limited in depth so that increased capacity could be realized. Itwould be further desirable for such data storage media to be written insuch a way that refractive index of the surrounding media is notsignificantly altered and that a substantial degradation of hologramefficiency at various depths is not seen. Desirably, any such materialsprovided would have sufficient refractive index change to supportdiffraction efficiencies so as to be capable of recording high-densitymicro-holographic data, thereby further expanding the storage capacityof the material.

BRIEF DESCRIPTION

In one embodiment an optical data storage medium is provided. Theoptical data storage medium includes a polymer matrix; a reactantcapable of undergoing a change upon triplet excitation, thereby causinga refractive index change; and a non-linear sensitizer capable ofabsorbing actinic radiation to cause upper triplet energy transfer tosaid reactant. The refractive index change capacity of the medium is atleast about 0.005. The non-linear sensitizer comprises a triarylmethanedye.

In another embodiment, an optical data storage is provided. The methodcomprises providing an optical data storage medium. The optical datastorage medium includes a polymer matrix; a reactant comprisingcinnamate, a cinnamate derivative and/or a cinnamamide derivativecapable of undergoing a change upon triplet excitation, thereby causinga refractive index change; and a non-linear sensitizer capable ofabsorbing actinic radiation to cause upper triplet energy transfer tosaid reactant. The refractive index change capacity of the medium is atleast about 0.005. The non-linear sensitizer comprises a triarylmethanedye.

In yet another embodiment, a method for optical data storage isprovided. The method comprises a first step of providing an optical datastorage medium. The optical data storage medium comprises a polymermatrix, a reactant capable of undergoing a change upon tripletexcitation, thereby causing a refractive index change and a non-linearsensitizer capable of absorbing actinic radiation to cause upper tripletenergy transfer to said reactant. The refractive index change capacityof the medium is at least about 0.005. The non-linear sensitizercomprises a triarylmethane dye. The method comprises a second step ofrecording a microhologram in said optical data storage medium.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a graphical depiction of the response of a linear sensitizerto actinic radiation;

FIG. 2 is a graphical depiction of the response of a thresholdsensitizer to actinic radiation;

FIG. 3 is a cross-sectional view of an optical storage media, showingthe area of impact of actinic radiation if the media comprises a linearsensitizer and the area of impact of actinic radiation if the mediacomprises a threshold sensitizer;

FIG. 4 is a schematic energy level diagram showing the upper tripletexcited state absorption and resulting energy transfer for a sensitizerexhibiting reverse saturable absorption;

FIG. 5 is a graphical depiction of the reflectivity of an array ofmicro-holograms recorded in an optical data storage media in accordancewith an embodiment of the invention; and

FIG. 6 is a graphical depiction of the sensitivity of one embodiment ofthe optical data storage medium as a function of intensity in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termsuch as “about” is not to be limited to the precise value specified. Insome instances, the approximating language may correspond to theprecision of an instrument for measuring the value. Similarly, “free”may be used in combination with a term, and may include an insubstantialnumber, or trace amounts, while still being considered free of themodified term.

As used herein, the terms “may” and “may be” indicate a possibility ofan occurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function. These terms may also qualifyanother verb by expressing one or more of an ability, capability, orpossibility associated with the qualified verb. Accordingly, usage of“may” and “may be” indicates that a modified term is apparentlyappropriate, capable, or suitable for an indicated capacity, function,or usage, while taking into account that in some circumstances themodified term may sometimes not be appropriate, capable, or suitable.For example, in some circumstances, an event or capacity can beexpected, while in other circumstances the event or capacity cannotoccur—this distinction is captured by the terms “may” and “may be”.

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” and “the,” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive, and mean thatthere may be additional elements other than the listed elements.Furthermore, the terms “first,” “second,” and the like, herein do notdenote any order, quantity, or importance, but rather are used todistinguish one element from another.

Embodiments of the invention described herein address the notedshortcomings of the state of the art. These embodiments advantageouslyprovide an improved optical data storage medium. In one embodiment anoptical data storage medium is provided. The optical data storage mediumincludes a polymer matrix; a reactant capable of undergoing a changeupon triplet excitation, thereby causing a refractive index change; anda non-linear sensitizer capable of absorbing actinic radiation to causeupper triplet energy transfer to said reactant. The refractive indexchange capacity of the medium is at least about 0.005. The non-linearsensitizer comprises triarylmethane dyes. Diffraction efficiency of theorder greater that about 1 percent is achievable using a relativelylower laser fluence of about 190 Joules per centimeter that what istypically used in the art, such as, a laser fluence of about 300 Joulesper centimeter to about joules per centimeter. This may be attributed tothe pre-alignment of the cinnamate pairs due to charge transferdonor-acceptor type of complex as described herein. Moreover thesensitivity of the optical storage medium is of the order of about 10⁻⁴square centimeters per Joule as obtained from quantum efficiency data.

As used herein, “diffraction efficiency” means a fraction of the beampower reflected by a hologram as measured at the hologram location withrespect to the incident probe beam power, while “quantum efficiency”means a probability of an absorbed photon to result in a chemical changethat produces a refractive index change. “Fluence” means the amount ofoptical beam energy that has traversed a unit area of the beamcross-section (measured, for example, in Joule per square centimeter),while “intensity” means optical radiative flux density, for exampleamount of energy traversing a unit area of beam cross-section in unittime (measured in, for example, Watt per square centimeter).

As used herein, the term “non-linear sensitizer” refers to a materialthat has a sensitivity having a dependence to the light intensity, i.e.,the sensitivity has to be high enough at the high (recording) intensity,and low enough at the lower (readout) intensity. For example, in asituation where the read intensity is about 20 to about 50 times lowerthan the write intensity, the sensitivity (based on a specificassumptions on the readout life time and/or number of readout cycles thematerial has to survive) may decrease by an order greater than about 10⁴times to about 10⁵ times the initial sensitivity. This difference in theintensity and sensitivity constitutes the amount of nonlinearity thematerial has to exhibit.

There is provided herein optical data storage media suitable forrecording microholographic data in a bit-wise approach. The mediadesirably exhibits a nonlinear response to actinic radiation, i.e.,experiences no substantial change in refractive index for incident laserlight below a threshold, and significant changes in refractive indexabove the threshold. Advantageously, recording into such a medium isonly possible with the light having a power, or intensity, exceeding athreshold value and the recorded data can be repeatedly andsubstantially non-destructively read with light having an intensitybelow the threshold. Microholograms recorded in the present optical datastorage media are expected to be smaller in size than the beam used torecord them.

In one embodiment, the optical data storage medium comprises anon-linear sensitizer and a reactant dispersed within a polymer matrixand can exhibit refractive index change suitable for the recordation ofmicroholograms at high data densities. In one embodiment, the refractiveindex change capacity of the medium is at least about 0.005. In oneembodiment, the refractive index change capacity is in a range of fromabout 0.005 to about 0.25. In yet another embodiment, the refractiveindex change capacity is in a range of from about 0.01 to about 0.2. Instill yet another embodiment, the refractive index change capacity is ina range of from about 0.005 to about 0.1.

Although other properties can also impact the ability of an optical datastorage media to record microholographic data in a bit-wise fashion,such as recording speed, recording intensity, and transparency to name afew, it is believed that the achievable diffraction efficiency and/orrefractive index change of a particular media will be controlling in theability of the media to record microholographic data in a bit-wisefashion. Because of the diffraction efficiencies achievable by thepresent optical data storage media, the media may be capable of storingabout 1 terabyte of information on a disk comparable in size to a singleCD or single DVD.

In one embodiment, the present media comprises reactants capable ofundergoing a change upon triplet excitation (T_(n); n>1). As usedherein, the term “change” is meant to include any indirect photochemicalreaction of the reactant, for example photodimerization orisomerization. Photodimerization is a bimolecular photochemical processinvolving an electronically excited unsaturated molecule that undergoesaddition with an unexcited molecule of a structurally similar and/oridentical species (e.g. two olefins combining to form a cyclobutane ringstructure). The covalent bonding that occurs in this reaction produces anew moiety which can be generally classified as a photoproduct. When theword “indirect” is used in conjunction with terms such asphotodimerization, photochemical reaction or photoreaction, it meansthat the reactant did not receive the energy directly from absorption ofa photon, but rather from another molecule (such as, for example, asensitizer or mediator) that first absorbed the photon and thentransferred a portion of that energy to the reactant that subsequentlyunderwent dimerization.

In certain embodiments, the reactants suitable for use in the opticaldata storage media described include may have the following propertiesand functionalities. In one embodiment, the reactants may be capable ofundergoing dimerization so that less volume change is required to gofrom reactant to product, for example, reactants that undergodimerization processes not by direct photoexcitation of the reactant butby indirect “non-radiative energy transfer” (in the present casetriplet-to-triplet energy transfer) pathway from the photoexcitedsensitizer to the reactant. The reactants wherein a nonlinear sensitizerreceives energy from a two-photon process and delivers that energy toone reactant that subsequently condenses with a second reactant toprovide a product. The reactants that, when derivatized on a polymerbackbone can provide a very large refractive index change, whichcorresponds to the available capacity of the material, for example, arefractive index change capacity of at least about 0.005 may be achievedif greater that about 85 percent of the reactants are converted toproduct. Finally, those that, when derivatized on a polymer backbone,are capable of undergoing both inter- and intramolecular condensationreactions, thereby accelerating the consumption thereof. The reactantsmay be capable of providing desired refractive index changes withincident fluence of less than 10 joules per square centimeter as aresult of higher quantum efficiency of the sensitized photo-reaction,which in turn may also provide greater diffraction efficiencies andshorter recording times.

In one embodiment, the linear sensitizer capable of absorbing actinicradiation may include cinnamate materials, cinnamate derivatives, andcinnamamide derivatives. In one embodiment, the cinnamate materials maybe capable of undergoing [2+2] indirect photodimerization and indirectphotopolymerization may be used. These cinnamate materials, due to theirtransparency (negligible ultraviolet absorption) at about 405 nanometersor at about 532 nanometers keep the linear bleaching of the cinnamate toa minimum and facilitate only the triplet-triplet energy transfer fromthe excited sensitizer. Any cinnamate material may be used, and those ofordinary skill in the art are aware of many suitable for use in theoptical data storage medium. In some embodiments, the cinnamatematerials will desirably comprise polyvinylcinnamates (PVCm) withcinnamate content of the polyvinyl backbone varying between about 54weight percent to about 75 weight percent based upon the total weight ofthe polyvinylcinnamate.

Examples of polyvinylcinnamates, cinnamate derivatives and cinnamamideanalogs include, but are not limited to, polyvinylcinnamate (PVCm),polyvinyl 4-chlorocinnamate (PV4-ClCm), polyvinyl 3-chlorocinnamate(PV3-ClCm), polyvinyl 2-chlorocinnamate (PV2-ClCm), polyvinyl4-methoxycinnamate (PV4-MeOCm), polyvinyl 3-methoxycinnamate(PV3-MeOCm), polyvinyl 2-methoxycinnamate (PV2-MeOCm), (2E,2′E)-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-chlorophenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-methoxyphenyl)acrylate).(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenyl)acrylamide(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-chlorophenyl)acrylamide),(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diaryl)bis(3-(4-methoxyphenyl)acrylamide.These are shown below:

Where R═H or Cinnamate X═H (Polyvinylcinnamate(PVCm),

OMe (Polyvinyl 4-methoxycinnamate(PV4-MeOCm), orCl (Polyvinyl 4-chlorocinnamate(PV4-ClCm)

Where X=(para)-H: (2E,2′E)-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenylacrylate) orX=(para)-Cl: (2E,2′E)-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-chlorophenyl)acrylate) orX=(para)-MeO:(2E,2′E)-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-methoxyphenyl)acrylate)

Where X=(para)-H:(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenyl)acrylamide) orX=(para)-Cl:(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-chlorophenyl)acrylamide)orX=(para)-MeO:(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-methoxyphenyl)acrylamide)

In one embodiment, the reactant(s) utilized in the present optical datastorage media are capable of undergoing a change upon tripletexcitation. Referring to FIG. 4, a schematic energy level diagram 400 isprovided. The diagram 400 shows the upper triplet T_(n) excited stateabsorption and resulting energy transfer for a sensitizer exhibitingreverse saturable absorption. The reactants used in the present opticaldata storage media have a triplet energy denoted by arrow 422 below thatof the T₂ state of the sensitizer denoted by arrow 424, but above thatof the T₁ state of the sensitizer, shown at arrow 426. The reactants arealso capable of receiving energy from an upper triplet state (T₂ orhigher) of the sensitizer, and undergoing a reaction to form a product,which provides a refractive index change within the polymer matrix andthus, a recorded hologram.

In addition to the aforementioned benefits, the use of such materials asthe reactant in the optical data storage media described herein may alsoprovide the possibility of a higher loading when derivatized on apolymer backbone than conventional reactants. For example, loading ofconventional reactants when derivatized on a polymer backbone may belimited to about 30 weight percent. In certain embodiments, reactantsdescribed herein may be loaded onto polymer backbones at much greaterloadings, i.e., up to about 90 weight percent, based upon the totalweight of the optical data storage media.

In certain embodiments, the use of the reactants provided herein providea significant decrease in birefringence as compared to conventionalreactants. In certain other embodiments, the optical recording mediadescribed provides the ability to rapidly create high-resolutionmicro-holograms with minimal heat formation and signal leakage toneighboring locations that can result in smearing of the capturedholographic pattern.

The reactant is usually present in relatively high concentrations bothto yield large changes in optical properties within the polymer matrixand to promote efficient triplet energy transfer. In one embodiment, thereactant may be present in the optical data storage media in amounts ina range from about 2 mole percent to about 90 mole percent, based uponthe total weight of the optical data storage media. In anotherembodiment, the reactant may be present in the optical data storagemedia in amounts in a range from about 5 mole percent to about 85 molepercent, based upon the total weight of the optical data storage media.In yet another embodiment, the reactant may be present in the opticaldata storage media in amounts in a range from about 10 mole percent toabout 80 mole percent, based upon the total weight of the optical datastorage media.

The reactant may be covalently attached, or otherwise associated with,the polymer matrix. For example, polymers functionalized with cinnamatesmay be utilized as the polymer matrix. In this case, In one embodiment,the optical data storage media may comprise higher loading amounts ofthe reactants, for example, up to about 90 weight percent, based uponthe total weight of the optical data storage media.

In addition to the reactants described above, the present optical datastorage media desirably comprises one or more non-linear sensitizers.The non-linear sensitizers are capable of absorbing incident actinicradiation, for example in the form of one or more photons, and thentransferring the energy to the reactant molecule to induce a molecularrearrangement of the reactant into a product that, in turn, gives riseto modulations in the refractive index of the medium. This modulationrecords both the intensity and phase information from the incidentactinic radiation as the hologram. The advantages of the use ofnonlinear (or “threshold”) sensitizers as opposed to linear sensitizerscan be further understood with references to FIGS. 1A, 1B, and 2.

Referring to FIG. 1 a graphical depiction 100 of the response of alinear sensitizer to actinic radiation is shown. The graph 100 includesa X-axis 110 representing fluence in joules per square centimeter and aY-axis 112 representing change in refractive index. The curve 114 showsthe response (maximum refractive index change) of a linearphotosensitive material to incident actinic radiation. Referring to FIG.2 a graphical depiction 100 of the response of a threshold material toactinic radiation is shown. The graph 200 includes a X-axis 210representing fluence in joules per square centimeter and a Y-axis 212representing change in refractive index. The curve 214 shows theresponse (maximum refractive index change) of a linear photosensitivematerial to incident actinic radiation. The continuously ascending curve114 in FIG. 1 illustrates that the linear photosensitive materials willcause a reaction at any power density (intensity) of recording light andthe amount of the refractive index change (delta n) achieved will be thesame for the same radiative energy (fluence) received by the material.In contrast, the curve 214 for threshold materials illustrated that thethreshold material will only cause a reaction at and over a certainlight intensity of recording light.

As a result, and as is shown in FIG. 3, in optical data storage media300 comprising linear photosensitive materials, consumption of dynamicrange will occur in non-addressed volumes, substantially everywhereactinic radiation passes through, shown as sections 310. In contrast, ifdata storage media 300 comprises threshold materials, consumption ofdynamic range in non-addressed volumes is reduced or eliminated andconsumption will occur substantially only in the target volume, i.e., atthe focal point 312 of the actinic radiation. The use of thresholdmaterials in the present optical data storage medium thus facilitatesrecording into a layer of bit-wise data buried in the bulk of the mediumwithout disruption of adjacent layers of previously recorded data orvacant space available for subsequent recording. Also, as the lightintensity in a tightly focused laser beam varies dramatically throughthe depth of the focal spot and is usually at its maximum at the beamwaist (narrowest cross section), the threshold response of the mediumwill naturally restrict material conversion to occur only in theimmediate vicinity of the beam waist. This may lead to a reduction inmicrohologram size within each layer, thus facilitating an increase inlayer data storage capacity of the present media, so that the overalldata storage capacity of the media may also be increased. The datastorage media will also advantageously be substantially stable inambient light, so that exposure to the same does not result insubstantial deterioration or damage to the media.

The nonlinear sensitizers used in the present optical data storage mediaare capable of transferring energy from an upper triplet state (T_(n),wherein n>1), which has a very short lifetime (nanoseconds to a few μ(micro) seconds), to the reactant. The ability to transfer energy fromthe T_(n) state provides the optical storage media provided herein withits nonlinear, threshold properties. That is, T_(n) excited stateabsorption is only appreciable when the sensitizer is excited byhigh-intensity light, for example light having an intensity at least 2orders of magnitude or more greater than ambient light, and negligiblysmall when subjected to low-energy radiation. This allows for thepresent optical data storage media, comprising the nonlinearsensitizers, to remain substantially transparent and inert to lowintensity radiation, for example, reading or ambient light, and to onlychange its properties (absorbance and thus, refractive index) inresponse to high energy recording light at or near the focal points. Asa result, the present optical data storage media exhibits the thresholdbehavior desired and/or necessary for the bit-wise recordation ofmicroholographic data.

FIG. 4 is a schematic energy level diagram showing the upper tripletT_(n) excited state absorption and resulting energy transfer for asensitizer exhibiting reverse saturable absorption. As shown in energylevel diagram 300, arrow 410 illustrates the ground state absorptioncross section of a photon as it transitions from the singlet groundstate S₀ to a first excited state S₁. The intersystem-crossing rate,represented by arrow 412, signifies the transfer of energy that occurswhen the sensitizer moves from an excited singlet state S₁ to acorresponding triplet state T₁. Arrow 414 indicates the excited tripletstate absorption cross section. Once the upper level triplet state T_(n)is achieved by subsequent linear absorption, two upper excited decayprocesses are possible. One possible decay process, denoted by arrow 416in FIG. 4, is the non-radiative relaxation by internal conversion (IC)to the lower lying T₁ state. The other possible decay process is denotedby arrow 418 in FIG. 4, and involves the release of energy from thesensitizer and the transfer of this energy to the reactant viatriplet-triplet energy transfer. The reactant then undergoes a changedenoted by arrow 420 to form the holographic grating and record thedata. The change in this case is a chemical reaction, and moreparticularly, a bimolecular photochemical process involving a cinnamatemolecule electronically excited to its triplet state undergoes additionwith a unexcited or a ground state cinnamate molecule to form acyclobutane ring structure.

In some embodiments, the present nonlinear sensitizers may absorb twophotons, typically, sequentially. Also, once the sensitizers describedherein transfer the absorbed energy to the reactant (as shown at 418,FIG. 4), they return to their original state, and may repeat the processmany times over. The sensitizers thus do not get substantially consumedover time, although their ability to absorb energy and release it to oneor more reactants may degrade over time. This is in contrast tomaterials known conventionally as photosensitive materials, which canabsorb energy (typically a single photon) and not transfer it to othermolecules, but undergo conversion to a new structure, or react withanother molecule to form a new compound in so doing.

In one embodiment, the nonlinear sensitizers comprise reverse saturableabsorbers (RSAs). For the purposes of this application, a reversesaturable absorber (RSA) is a compound that has extremely low linearabsorption at a given wavelength (such as 532 or 405 nanometers) andtransmits nearly all of the light. However, when subjected to highintensity laser power at these given wavelengths, low level linearabsorption can lead to a state where the molecule has a higherabsorption cross section and becomes highly absorbing at that samewavelength; causing it to strongly absorb subsequent photons. Thisnonlinear absorption is often referred to as sequential two-photonabsorption. Examples of RSAs suitable for use in the present opticaldata storage media are disclosed in Perry et al., “Enhanced reversesaturable absorption and optical limiting in heavy atom-substitutedphthalocyanines”, Optics Letters, May 1, 1994, Vol. 19, No. 9, pages625-627, hereby incorporated by reference herein in its entirety.

Many RSAs experience photoexcitation when impinged upon by incidentactinic radiation having a wavelength of 532 nanometers. Because thiswavelength is within the green color portion of the visible spectrum,these RSA's may typically be referred to as “green” RSA's. Any of thesegreen RSA's that are capable of entering into the upper triplet (T₂)state upon photoexcitation may be utilized in the present optical datastorage media. In one embodiment, the RSA is a triarylmethane dye.Suitable examples of triarylmethane dyes include the dyes listed inTable I below

S. No. Dyes Chemical Structure 1 Chloride, Bromide or Iodide salt ofEthyl Violet

2 Chloride, Bromide, or Iodide salt of crystal violet

3 Rose Bengal

4 Rhodamine 123

5 Pyronin Y dyes

6 Crystal Violet Lactone

7 Eosin Y

The amount of nonlinear sensitizer used in the optical data storagemedia may depend on its optical density at the wavelength of light usedto record the hologram. Solubility of the sensitizer may also be afactor. In one embodiment, the sensitizer may be used in an amount fromabout 0.002 weight percent to about 15 weight percent, based upon thetotal weight of the data storage media. In another embodiment, thesensitizer may be used in an amount of from about 0.01 weight percent toabout 4.5 weight percent. In yet another embodiment, the sensitizer maybe used in an amount of from about 1 weight percent to about 5 weightpercent.

In certain embodiments, photostabilizers may also be included in theoptical data storage media described herein. Typically, the photostabilizers assist in the photostabilization of the non-linearsensitizer utilized herein. Those of ordinary skill in the art are awareof compounds/materials useful for this purpose, and useful amounts ofthese, and any of these may be used, in any suitable amount. In oneexemplary embodiment, the compound that may assist in thephotostabilization of a phthalocyanine dye, for example, includesbisdithiobenzil nickel.

Optionally, the data storage media may further comprise a mediator toassist in upper triplet energy transfer from the sensitizer to thereactant. The triplet state (T_(1m)) of the mediator will desirably be(a) below the triplet state (T_(n); n>1) of the sensitizer but above theT₁ of the sensitizer and (b) above the triplet state (T_(1r)) of thereactant, or ideally between about 50 kilocalories per mole to about 90kilocalories per mole.

In certain embodiments, where the mediator is employed, presence ofmediator in the samples may help in improving the sensitivity at writeintensities. One of the factors that may limit the sensitivity inenergy-transfer systems is a larger energy difference between the T₂state of the RSA dye (Ethyl violet, of about 110) and the T₁ state(about 58 kilocalories per mole) of the acceptor (cinnamate) moleculeabout 52 kilocalories per mole. The Tripet-Triplet Energy Transfer(TTET) is typically found to be more efficient only when theDonor-Acceptor energy difference is less than about 20 kilocalories permole. In order to overcome this limitation, we use a mediator—a moleculethat does not absorb light directly, but participate in the energytransfer by receiving the energy from the RSA dye molecules andtransferring it further to the index change material molecules with theefficiency that is higher than that of the direct transfer from thesensitizer to the acceptor. The mediator is chosen such that its tripletenergy (T₁) is below the T₂ state of the RSA dye but above the acceptorT₁ state. Being a nonlinear function of the donor-acceptor energydifference, the resulting efficiency of two sequential energy transferprocesses (donor→mediator→acceptor) may be more efficient than adirector donor→acceptor transfer.

Examples of suitable mediators include, but are not limited to,acetophenone (T₁˜78 kilocalories per mole), dimethylphthalate (T₁˜73kilocalories per mole), propiophenone (T₁˜72.8 kilocalories per mole),isobutyrophenone (T₁˜71.9 kilocalories per mole),cyclopropylphenylketone (T₁˜71.7 kilocalories per mole), deoxybenzoin(T₁˜71.7 kilocalories per mole), carbazole (T₁˜69.76 kilocalories permole), diphenyleneoxide (T₁˜69.76 kilocalories per mole),dibenzothiophene (T₁˜69.5 kilocalories per mole), 2-dibenzoylbenzene(T₁˜68.57 kilocalories per mole), benzophenone (T₁˜68 kilocalories permole), polyvinylbenzophenone (T₁˜68 kilocalories per mole),1,4-diacetylbenzene (T₁˜67.38 kilocalories per mole), 9H-fluorene (T₁˜67kilocalories per mole), triacetylbenzene (T₁˜65.7 kilocalories permole), thioxanthone (T₁˜65.2 kilocalories per mole), biphenyl (T₁˜65kilocalories per mole), phenanthrene (T₁˜62 kilocalories per mole),phenanthrene (T₁˜61.9 kilocalories per mole), flavone (T₁˜61.9kilocalories per mole), 1-napthonirile (T₁˜57.2 kilocalories per mole),poly (β-naphthoylstyrene) (T₁˜55.7 kilocalories per mole), Fluorenone(T₁˜55 kilocalories per mole), and combinations thereof.

If utilized, the mediator may, if desired, be covalently attached to, orotherwise associated with, the polymer matrix. Incorporating themediator into the polymer matrix in this way can allow for higherconcentrations of the mediator to be utilized, which, in turn, canincrease recording efficiency of the data storage media.

The amount of mediator used, if any, should not be so much as to causeself-quenching, i.e., when two triplets of the mediator meet each otherto generate a singlet state and a ground state of the mediator. Optimalamounts of any mediator may also depend on the particular sensitizer. Inone embodiment, if the mediator is dispersed within the polymer matrixthe mediator may be present in an amount in a range from about 1 weightpercent to about 20 weight percent in the polymer matrix. In anotherembodiment, the mediator may be present in an amount in a range fromabout 1.5 weight percent to about 10 weight percent in the polymermatrix. In yet another embodiment, the mediator may be present in anamount in a range from about 2 weight percent to about 8 weight percentin the polymer matrix. In one embodiment, if the mediator is covalentlyattached to the polymer matrix the mediator may be present in an amountin a range from about 2 weight percent to about 50 weight percent in thepolymer matrix. within the polymer matrix. In another embodiment, themediator may be present in an amount in a range from about 5 weightpercent to about 40 weight percent in the polymer matrix. In yet anotherembodiment, the mediator may be present in an amount in a range fromabout 4 weight percent to about 30 weight percent in the polymer matrix.

The desired sensitizer and reactant may be substantially uniformlydispersed through a polymer matrix, or may be dispersed in any fashionso that bit-wise data recordation is facilitated within the medium. Thepolymer matrix may comprise a linear, branched or cross-linked polymeror co-polymer. Any polymer may be used so long as the sensitizer andreactant can be substantially uniformly dispersed therein. Further, anypolymer utilized will desirably not substantially interfere with theupper triplet energy transfer process. The polymer matrix may desirablycomprise a polymer that is optically transparent, or at least has a hightransparency at the wavelength contemplated for recording and readingthe optical data storage medium.

Particular examples of suitable polymers for use in the polymer matrixinclude, but are not limited to, poly(alkyl methacrylates), such aspoly(methyl methacrylate) (PMMA), polyvinyl alcohols, poly(alkylacrylates), polystyrenes, polycarbonates, polyacrylates, poly(vinylidenechloride), poly(vinyl acetate), and the like. As mentioned above, thesensitizer may also be covalently attached, or otherwise associatedwith, the polymer matrix. For example, polymers such as polyesters,polycarbonates and polyacrylates including stilbene are readilyavailable, or, are readily functionalized to include stilbene units.

The polymer matrix may also contain a plasticizer, such as dibutylphthalate, dibutyl sebacate or di(2-ethylbexy) adipate. Plasticizers canenhance recording efficiencies by facilitating molecular motion. Typicalplasticizer levels may be in a range from about 1 weight percent toabout 20 weight percent, or from about or from about 2 weight percent toabout 10 weight percent, based upon the total weight of the storagemedia.

The optical data storage media described herein may be in aself-supporting form. Or, the data storage media may be coated onto asupport material, such as polymethyl(methacrylate) (PMMA),polycarbonate, poly(ethylene terephthalate), poly(ethylene naphthalate),polystyrene, or cellulose acetate Inorganic support materials such asglass, quartz or silicon may also be used, in those embodiments whereinuse of a support material may be desired.

In such embodiments, the surface of the support material may be treatedin order to improve the adhesion of the optical data storage media tothe support. For example, the surface of the support material may betreated by corona discharge prior to applying the optical data storagemedia. Alternatively, an undercoating, such as a halogenated phenol orpartially hydrolyzed vinyl chloride-vinyl acetate copolymer can beapplied to the support material to increase the adhesion of the storagemedia thereto.

Generally speaking, the optical data storage media described herein canbe prepared by blending the desired sensitizer, reactant, mediator (ifdesired) and polymer matrix. Proportions of these may vary over a widerange, and the optimum proportions and methods of blending may bereadily determined by those of ordinary skill in the art. For example,the sensitizer may be present in concentrations of from about 0.01weight percent to about 90 weight percent, and the reactant may bepresent in concentrations of from about 2 weight percent to about 80weight percent, or even up to about 90 weight percent, based upon thetotal weight of the optical data storage media.

EXAMPLES

Starting materials were bought commercially or made from known methods.For substituted and unsubstituted polyvinylcinnamate synthesis thestarting materials Cinnamoyl chloride, oxalyl chloride, p-methoxycinnamic acid, p-chloro cinnamic acid were obtained from commercialsource (all Aldrich), Polyvinylcinnamate was also obtained fromcommercial source (Scientific Polymer) were used as received.

Example 1-2 (E-1 to E-2) Synthesis of Polyvinyl Alcohol-Appended-withCinnamoyl Chloride Derivatives

To a 250 milliliters round bottom flask were added polyvinyl alcohol, 88percent hydrolysed (1.4 grams, 0.0292 moles repeat unit) and 25milliliters of N-methyl pyrrolidinone. The resultant mixture was heatedto about 80 degrees Celsius under an atmosphere of nitrogen for about 2hours. The heating resulted in the complete dissolution of polyvinylalcohol. The resultant mixture was cooled to about 50 degrees Celsius.The cinnamoyl chloride derivatives were added in portions as a solidover a period of about two hours. After the addition was complete themixture was stirred for about one more hour at about 50 degrees Celsius.The resultant mixture was precipitated into a blender containing 75milliliters of methanol. The resulting solid was collected by suctionfiltration then dissolved in 30 milliliters of methylene chloride andagain precipitated into 75 milliliters of methanol. The resulting solidwas dried in a vacuum oven at room temperature for 4 hours thenovernight at 50 degrees Celsius. The quantities of various reactantsadded is included below in Table 1.

TABLE 1 Moles of cinnamoyl derivative Examples 4-methoxy cinnamoylchloride cinnamoyl chloride E-1 0.43 0 E-2 0 0.43

Comparative Examples 1-2 (CE-1 and CE-2) Synthesis of BoronSubphthalocyanine 3-Iodo-5-Glutarylphenoxide (subPC)-Appended-withCinnamoyl Chloride Derivatives

To 250 milliliters round bottom flask were added polyvinyl alcohol, 88percent hydrolysed (1.4 grams, 0.0292 moles repeat unit) and 25milliliters of N-methyl pyrrolidinone. The resultant mixture was heatedto about 80 degrees Celsius under an atmosphere of nitrogen for about 2hours. The heating resulted in the complete dissolution of polyvinylalcohol. The resultant mixture was cooled to about 50 degrees Celsius.The cinnamoyl chloride derivatives were added in portions as a solidover a period of about two hours. After the addition of about 40 molepercent of the cinnamoyl chloride derivatives was completed, in eachexample, a 2 milliliters of a corresponding weight percent solution ofBoron subphthalocyanine 3-iodo-5-glutarylphenoxide acid chloride inmethylene chloride was added to the mixture (subPC). After the rest ofcinnamoyl chloride was added the mixture was stirred for about one morehour at about 50 degrees Celsius. The resultant mixture was precipitatedinto a blender containing 75 milliliters of methanol. The resultingsolid was collected by suction filtration then dissolved in 30milliliters of methylene chloride and again precipitated into 75milliliters of methanol. The resulting solid was dried in a vacuum ovenat room temperature for 4 hours then overnight at 50 degrees Celsius.The quantities of various reactants added is included below in Table 2.

TABLE 2 Moles of cinnamoyl derivative Boron subphthalocyanine 3-4-methoxy iodo-5-glutarylphenoxide cinnamoyl cinnamoyl acid chlorideappended Examples chloride chloride (moles) CE-1 0.43 0 0.0003 CE-2 00.43 0.00017

Example 3-10 (E-3 to E-10) Preparation of Polymer Film from Poly VinylAlcohol-Appended-with Cinnamoyl Chloride Derivatives Prepared in E-1 andE-2 for use in Quantum Efficiency Studies

A 2.2 weight percent solution of PV4-MeOCm and PVCm prepared in E-1 andE-2 respectively, independently doped with 0.04 moles triarylmethane dyein tetrachloroethane was prepared. In some examples a mediator wasadded. The contents were dissolved by heating the solution on a hotplate at about 70 degrees Celsius. The solution was filtered through a0.45 micrometer Whatman filter. The filtered solution was poured onto a50 millimeters×25 millimeters microscopic slide and the solution wasspin casted on a spin coater at about 2000 revolutions per minute for 30seconds. Then the slide was dried for about 20 minutes to about 30minutes in an oven at a temperature of about 70 degrees Celsius. Thethickness of the polymer film formed was approximately about 100nanometers. The dye and the mediator used, and the amount of dye dopedis provided in Table 3 below. The quantum efficiency measurements thatprovide the sensitivity at write and read intensities are also providedin Table 3.

To define the quantum efficiency (QE) and sensitivity of our energytransfer (ET) process the optical setup described below was used. Thesetup consists of two light sources one from the UV-Vis lamp and otherfrom the optical parametric oscillator (OPO). Due to materialcharacteristics the index change material has maximum absorbance at 280nanometer. The UV probe chosen had a wavelength in a range of about 280nanometers to about 320 nanometers. 405 nanometers wavelength was usedfrom the output of OPO system as pump exposure source as the RSA dye issupposed to have a small portion of absorption in the 405 nanometerswavelength.

TABLE 3 Sensitivity Sensitivity Weight @write @Read percent of Mediatorintensity 264 intensity 0.5 PVCm/PV4- weight Weight megawatt per Wattsper MeOCm percent percent of square square Example Polymer appended Dyedoped dye doped centimeter centimeter E-3 PVCm 68 Rose Bengal 0 2.916.12 × 10⁻⁷  7.8 × 10⁻⁷ Tetra butyl- ammonium salt E-4 PVCm 68 RoseBengal 0 3.89 3.56 × 10⁻⁶  7.5 × 10⁻⁶ lactone E-5 PVCm 68 Eosin-Y 02.59( 1.36 × 10⁻⁷ 1.96 × 10⁻⁸ E-6 PVCm 68 Crystal Violet 0 1.66  8.5 ×10⁻⁷ 3.83 × 10⁻⁶ Lactone E-7 PVCm 68 Ethyl Violet 0 1.97  8.8 × 10⁻⁵ 1.25 × 10⁻¹⁰ chloride salt E-8 PV4- 68 Ethyl Violet 0 1.97 3.15 × 10⁻⁴— MeOCm chloride salt E-9 PV4- 68 Ethyl Violet 4 1.97 7.34 × 10⁻⁴ —MeOCm chloride salt (benzophenone)  E-10 PV4- 68 Ethyl Violet 6 (4- 1.978.84 × 10⁻⁴ — MeOCm chloride salt Piperdinoacetopheone)

The film samples prepared in E-3 to E-10 were tested for non-linear orthreshold property during the triplet energy transfer from the highertriplet states (T_(n)>1) to the cinnamate. As seen form data provided inTable 3, among the different dyes tested for the PVCm material, based onquantum efficiency measurements, ethyl violet chloride salt gavesensitivity values of about 8.8×10⁻⁵. Most importantly the differencebetween the READ and WRITE sensitivity is 5 orders of magnitudedifferent (8.8×10⁻⁵ and 1.25×10⁻¹⁰) in the case of ethyl violet, whichis very important parameter as it shows that the ethyl violet/PVCmsystem may be very stable to low intensity (ambient) light but will workvery efficiently during writing process with a high intensity laser.Additionally the sensitivities further increased as shown in E-9 andE-10 when mediators were used.

Example 11 (E-11) Preparation of Polymer Film from Poly VinylAlcohol-Appended-with Cinnamoyl Chloride Derivatives Prepared in E-1 andE-2 for use in Holographic Studies

Thick film samples for demonstrating microholograms and recording thereflectivity after writing microholograms were prepared as follows. A 10weight percent solution of 1 gram of PVCm (prepared in E-2) doped with0.04 moles triarylmethane dye (for example ethyl violet chloride salt)and 4 weight percent (40 milligrams, with respect to the polymer) ofmediator benzophenone in methylene chloride:dichloroethane (9:1) wasprepared. The solution was filtered through 0.45 micron Whatman syringefilter. The solution was then solvent casted onto a (5 centimeters×5centimeters) pyrex glass by containing the solution on to a circularglass rim. The whole of the above set-up was placed on a hot plate setat 45 degrees Celsius. The sample was covered with an inverted glassfunnel covering the whole sample and the opening of the tip of thefunnel was covered with a Kimwipe to maintain slow evaporation of thesolvent. The solvent was made to evaporate over a period of about 24hours to about 48 hours. The solution was filtered through a 0.45micrometer Whatman filter. Later the sample coated on to the glass platewas taken into a vacuum oven and dried at 65 degrees Celsius for 3 to 4days to drive out the residual solvents. The thickness of the polymerfilm formed was approximately about 300 micrometers to about 320micrometers.

Experimental Demonstration of Micro-Hologram Recording in the PresentOptical Data Storage Media was Performed Using a Micro-HolographicStatic Tester System.

405 nanometers Apparatus: A tunable optical parametric oscillator systemoperating at the 405 nanometers wavelength was used as a pulsed lightsource for recording and readout of micro-holograms. The light wasfocused into the medium sample using optics with numerical aperture (NA)of 0.16, resulting in the approximate dimensions of the recording volumeto be 1.6×1.6×17 micrometers. The pulse energies used for micro-hologramrecording were between tens to hundreds of nano-Joules, which allowedone to achieve light intensity values of hundreds of megawatts persquare centimeter to several gigawatts per square centimeter at thefocal spot of such focused recording beam. The readout of the lightreflected from micro-holograms was done using the same beam attenuatedby approximately 100 to 1000 times with respect to the recording power.

Using the system appropriate for the sensitizer, the recording ofmicroholograms in the optical data storage media was performed by twohigh-intensity counter-propagating pulsed recording beams focused andoverlapped in the bulk of the recording medium to produce the intensityfringe pattern consisting of light and dark regions (fringes). Theilluminated regions of the interference pattern undergo a change asdescribed above, which results in a locally modified refractive index ofthe material, while the dark regions remain intact, thus creating avolume hologram. The present optical data storage media is sensitive toa high-intensity light and is relatively inert to the low-intensityradiation. The power of the recording beam was adjusted so that thelight intensity near the focal region of the beam is above the recordingthreshold (above which the change readily occurs), while remaining lowoutside the recordable region away from the focal spot of the beam, thuseliminating unintended media modification (recording or erasure).

During microhologram recording, the primary recording beam was splitinto the signal and the reference using a half-wave plate (π/2) and afirst polarization beam splitter. The two secondary beams were steeredto the sample in a counter-propagating geometry and were focused tooverlap in the bulk of the optical data storage media by identicalaspheric lenses with a numerical aperture (NA) of up to 0.4. Thepolarization of both beams was converted into circular polarization—withtwo quarter-wave plates (π/4) to ensure that the beams interfere tocreate a high-contrast fringe pattern. The sample and the signal beamlens were mounted on closed-loop three-axis positioning stages with 25nanometers resolution. A position-sensitive detector on the referenceside of the sample was used to align the signal lens for optimizedoverlap of the focused signal and reference beams in the medium, andthus, optimized recording.

A variable attenuator and the half-wave plate/PBS assembly were used tocontrol the power level during recording and/or read-out. This allowsthe micro-holographic recording characteristics of the optical datastorage media to be measured as a function of the recording power and/orenergy. This functional dependence distinguishes between a linearoptical data storage medium/recording, where the strength of therecorded hologram is largely defined by the total amount of light energyreceived by the medium, but is independent of the light intensity, and anonlinear, threshold optical data storage medium/recording, where therecording efficiency is highly dependent upon the intensity of thelight. In a linear medium, a small exposure results in a low-strengthhologram, which gradually grows with higher exposures. In contrast, in anonlinear, threshold medium, recording is only possible with intensityexceeding the threshold value.

During read-out, the signal beam was blocked, and the reference beam wasreflected by the microholograms in the direction opposite to theincident direction. The reflected beam was coupled out from the incidentbeam path using the quarter-wave plate and a second polarizing beamsplitter, and was collected on a calibrated photodiode in a confocalgeometry to provide an absolute measure of the diffraction efficiency.By translating the sample with respect to the readout optics, it waspossible to obtain a 3D profile of a micro-hologram diffraction responseand evaluate dimensions of a micro-hologram.

FIG. 5 is a graphical depiction of the reflectivity of an array ofmicro-holograms recorded on the sample prepared in Example 11. The graph500 shows percentage reflectivity on the Y-axis 512 and the lateralposition in micrometers on the X-axis 510. The reflectivity valuesreached 0.012 percent at intensities of about 360 megawatts per squarecentimeter.

Example 12-13 (E-12 and E-13) and Comparative Examples 3-4 (CE-3 andCE-4) Preparation of Polymer Film from Polyvinyl Alcohol-Appended-withCinnamoyl Chloride Derivatives Prepared in E-1 and E-2 and from BoronSubphthalocyanine 3-Iodo-5-Glutarylphenoxide-Appended-with CinnamoylChloride Derivatives for Use in Comparative Studies for Sensitivity

The films were prepared in a similar manner as described for Examples3-10 above. Table 4 shows a comparison of the films prepared in CE-3with that prepared in E-12 and the film prepared in CE-4 with thatprepared in E-13. For a similar loading levels the sensitivity valuesare couple of orders of magnitude better for ethyl violet dyes comparedto the subphthalocyanine dyes. The sensitivity was tested at a constantintensity of 360 megawatts.

TABLE 4 Sensitivity @write Weight Weight intensity percent ofBenzophenone percent of 264 Fluence PVCm/PV (weight dye megawatt (joulesper 4-MeOCm percent) doped/ per square square Example Polymer appendedDye doped appended centimeter centimeter) E-12 PV4- 68 Ethyl Violet 4 2 4.5 × 10⁻⁵ 3.5 MeOCm chloride salt (doped) E-13 PVCm 68 Ethyl Violet 42 2.00 × 10⁻⁵ 5 chloride salt (doped) CE-3 PV4- 68 SubPC 4 1.7 5.12 ×10⁻⁶ 100 MeOCm (appended) CE-4 PVCm 68 SubPC 4 2 5.50 × 10⁻⁶ 133(appended)

FIG. 6 is a graphical depiction of the sensitivity of one embodiment ofthe optical data storage medium as a function of intensity for fixedrecording fluences of 3.5 joules per square centimeter and 5 joules persquare centimeter in accordance with an embodiment of the invention. Thegraph 600 shows sensitivity in square centimeters per joule on theY-axis 612 and intensity in megawatts per square centimeter on theX-axis 610. The curve 614 shows the sensitivity recorded at a fixedfluence of 3.5 joules per square centimeter for the film sample preparedin Example 12. The curve 616 shows the sensitivity recorded at a fixedfluence of 5 joules per square centimeter for the film sample preparedin Example 13. As can be seen in FIG. 6, the sensitivities reachedvalues of 4×10⁻⁵ square centimeters per joule at intensities of about360 megawatts per square centimeter. As is evident from FIG. 6 and fromTable 4, the samples with the ethyl violet dye show higher value ofsensitivity at even lower fluences than for the samples with subPC dye.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. An optical data storage medium comprising: a polymer matrix; areactant capable of undergoing a change upon triplet excitation, therebycausing a refractive index change; and a non-linear sensitizer capableof absorbing actinic radiation to cause upper triplet energy transfer tosaid reactant; wherein the refractive index change capacity of themedium is at least about 0.005; and wherein the non-linear sensitizercomprises a triarylmethane dye.
 2. The optical data storage medium ofclaim 1, wherein the refractive index change of the medium is at least0.05.
 3. The optical data storage medium of claim 1, wherein thereactant comprises a cinnamate, cinnamate derivative, cinnamamidederivative, or a combination thereof.
 4. The optical data storage mediumof claim 3, wherein the reactant comprises polyvinylcinnamate (PVCm),polyvinyl 4-chlorocinnamate (PV4-ClCm), polyvinyl 3-chlorocinnamate(PV3-ClCm), polyvinyl 2-chlorocinnamate (PV2-ClCm), polyvinyl4-methoxycinnamate (PV4-MeOCm), polyvinyl 3-methoxycinnamate(PV3-MeOCm), polyvinyl 2-methoxycinnamate (PV2-MeOCm),(2E,2′E)-((1S,2S)-cyclo hexane-1,2-diyl)bis (3-phenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-chlorophenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-methoxyphenyl)acrylate).(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenyl)acrylamide(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-chlorophenyl)acrylamide),(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diaryl)bis(3-(4-methoxyphenyl)acrylamide, or a combination thereof.
 5. The opticaldata storage medium of claim 1, wherein the medium is capable of storingmicroholographic data.
 6. The optical data storage medium of claim 1,further comprising a mediator capable of transferring energy between thenon-linear sensitizer and the reactant.
 7. The optical data storagemedium of claim 6, wherein the mediator comprises acetophenone,dimethylphthalate, benzophenone, 9H-fluorene, biphenyl, phenanthrene,1-napthonitrile, or a combination thereof.
 8. The optical data storagemedium of claim 1, wherein the non-linear sensitizer comprises asequential two-photon absorption process by a reverse saturableabsorber.
 9. The optical data storage medium of claim 8, wherein thenon-linear sensitizer comprises from ethyl violet, crystal violet, roseBengal, Rhodamine 123, Pyronin Y, or crystal violet lactone.
 10. Theoptical data storage medium of claim 1, further comprising a photostabilizer.
 11. The optical data storage medium of claim 10, wherein thephotostabilizer comprises bisdithiobenzil nickel.
 12. The optical datastorage medium of claim 1, wherein the polymer matrix comprises one ormore polyvinylalcohol, poly(alkyl methacrylates), poly(alkyl acrylates),polystyrenes, polycarbonates, polyacrylates, poly(vinylidene chloride),poly(vinyl acetate), or a combination thereof.
 13. The optical datastorage medium of claim 1, wherein the reactant and non-linearsensitizer are distributed substantially homogenously throughout thepolymer matrix.
 14. An optical data storage medium for the bit-wiserecording of microholographic data comprising: a polymer matrix; areactant comprising cinnamate, a cinnamate derivative and/or acinnamamide derivative capable of undergoing a change upon tripletexcitation, thereby causing a refractive index change; and a non-linearsensitizer comprising a reverse saturable absorber capable of absorbingactinic radiation to cause upper triplet energy transfer to saidreactant; wherein the refractive index change capacity of the medium isat least about 0.005; and wherein the non-linear sensitizer comprises atriarylmethane dye.
 15. The optical data storage medium of claim 14,wherein the refractive index change of the medium is at least about0.05.
 16. The optical data storage medium of claim 14, wherein thereactant comprises polyvinylcinnamate (PVCm), polyvinyl4-chlorocinnamate (PV4-ClCm), polyvinyl 3-chlorocinnamate (PV3-ClCm),polyvinyl 2-chlorocinnamate (PV2-ClCm), polyvinyl 4-methoxycinnamate(PV4-MeOCm), polyvinyl 3-methoxycinnamate (PV3-MeOCm), polyvinyl2-methoxycinnamate (PV2-MeOCm),(2E,2′E)-((1S,2S)-cyclohexane-1,2-diyl)bis (3-phenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-chlorophenylacrylate),(2E,2′E)-(1S,2S)-cyclohexane-1,2-diyl)bis(4-methoxyphenyl)acrylate).(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-phenyl)acrylamide(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diyl)bis(3-(4-chlorophenyl)acrylamide),(2E,2′E)-N,N′-((1S,2S)-cyclohexane-1,2-diaryl)bis(3-(4-methoxyphenyl)acrylamide, or a combination thereof.
 17. Theoptical data storage medium of claim 14, wherein the non-linearsensitizer is selected from ethyl violet, crystal violet, rose Bengal,Rhodamine 123, Pyronin Y, and crystal violet lactone.
 18. The opticaldata storage medium of claim 14, further comprising a mediator capableof transferring energy between the non-linear sensitizer and thereactant.
 19. The optical data storage medium of claim 18, wherein themediator comprises acetophenone, dimethylphthalate, benzophenone,9H-fluorene, biphenyl, phenanthrene, 1-napthonitrile, or a combinationthereof.
 20. A method for optical data storage comprising: providing anoptical data storage medium comprising a polymer matrix, a reactantcapable of undergoing a change upon triplet excitation, thereby causinga refractive index change and a non-linear sensitizer capable ofabsorbing actinic radiation to cause upper triplet energy transfer tosaid reactant, wherein the refractive index change capacity of themedium is at least about 0.005, wherein the non-linear sensitizercomprises a triarylmethane dye; and recording a microhologram in saidoptical data storage medium.